.Iadd.This application for reissue is a continuation of my copending application for reissue Ser. No. 211,418 filed Nov. 28, 1980, now abandoned. .Iaddend.
1. Field of the Invention
The present invention relates to fluid devices and particularly to those of the axial piston type which may function either as a fluid pump or as a fluid motor.
2. Description of the Prior Art
Heretofore, fluid pumping or motoring devices of the axial piston type have been constructed of a metallic housing having a revolving cylinder barrel with a plurality of parallel cylinder bores herein, within which pistons are reciprocated by means of a thrust plate assembly or the like. A rotary valve mechanism in the form of cylinder ports at one end of the cylinder barrel alternately connects each cylinder bore with an inlet and an outlet passage of the device as the cylinder barrel is rotated.
The thrust plate assembly in fluid devices of the variable displacement type normally takes the form of a yoke having transversely extending pintles rotatably carried in bearings suitably mounted to the wall of the housing such that the entire force exerted against the thrust plate assembly due to the fluid pressure acting against the piston within the cylinder barrel bores is taken by the housing, thus necessitating a strong metal housing. Such metal housings are expensive in that they must be cast molded and subsequently require a machining operation to provide the necessary precision that is needed in such constructions. It would be desirable to provide a housing for such axial piston fluid devices, constructed of a plastic material which would eliminate the subsequent machining operations and the resulting expenses normally incurred in using such metal housings. For example, housings constructed for fluid devices having the same displacement capacity would cost approximately $2.00 for a metal housing as compared to $.60 for a housing constructed of a plastic material. The equipment needed to manufacture a metal housing costs approximately $750,000.00 as compared to $3,500.00 for an injection mold which would be used in constructing a housing of a plastic material.
Further, heretofore fluid devices of the variable displacement type have used a thrust plate assembly which is normally of a metal construction such as cast iron or steel which, in addition to requiring substantial machining, adds to the overall weight of the device. It would be desirable to replace such cast iron and/or steel thrust plate assemblies with one constructed of a sintered material which, heretofore, has not been possible because of the high loads and complicated shape that such thrust plate assemblies require.
In addition to the high loads transmitted to the thrust plate assembly, suitable means must be provided which permit an easy movement of the thrust plate assembly with respect to the longitudinal axis of the drive shaft on which the cylinder barrel is rotated so as to vary the amount of reciprocal stroking movement imparted to the pistons within the cylinder bores to thereby permit a selected variation in the displacement of such axial piston fluid devices.
In such previously constructed axial piston fluid devices, the displacement control mechanism used to control the inclination of the thrust plate assembly with respect to the longitudinal axis of the drive shaft has necessitated a different design for both the fixed displacement device and the variable displacement pump as the displacement control mechanism is normally constructed as part of the housing in such variable displacement devices, thus requiring a larger housing for the variable displacement device. Heretofore, if the same housing were used for both variable and fixed displacement units, a larger housing would have been required since portions thereof would be used to mount the displacement control mechanism. The use of such a variable displacement housing in a fixed displacement unit results in an unduly large unit in proportion to its displacement. It would therefore be desirable to provide a housing which is constructed for both variable displacement and fixed displacement devices without requiring a larger housing for the variable displacement design.
It is also a conventional practice that such previously used devices have been normally constructed to use only one type of displacement varying control mechanism, whereas it may be desirable to have a fluid device having a housing construction which is adaptable for use with manual controls, pressure compensated controls and the like, thus eliminating the necessity of having several different housing designs for the same capacity unit so as to accommodate different displacement control applications.
Fluid devices of the axial piston type normally are characterized by having a valving face formed by a flat surface on which the cylinder barrel normally runs in abutment and in a fluid sealing relationship. The abutting face of the cylinder barrel on which the cylinder ports are disposed normally has been provided with arcuately spaced elevated pressure pads disposed radially outwardly from the cylinder ports providing a bearing surface on which the cylinder barrel rides in a manner which avoids excessive wear. Such bearing pads are more commonly referred to as "Kingsbury Pads" and have functioned in an acceptable manner in the past to compensate for wear and variations in oil viscosity due to changing temperatures and different fluids. In devices of this type operating at high speeds and high pressures, considerable difficulty may be experienced in providing a satisfactory running surface between the cylinder barrel and the valving face due to a lack of oil flow across the face of the cylinder barrel from the cylinder ports to the Kingsbury pads.
It would therefore be desirable to provide a new and improved Kingsbury pad for such axial piston fluid devices.
As speed and pressure is increased in such previously used fluid devices, there is always an accompanying increase in noise. This general increase in noise with increased speed and pressure may be attributed to a number of factors in devices of the axial piston type. First, the sound frequencies generated by the device increase with speed as the components of the device are subjected to increased alternating impact forces; second, the intensity of speed related sounds increases as the impact forces between components of the device increase; and third, the excitation spectrum of the significant piston harmonics also broadens, thus increasing the number of resonant responses.
It would therefore be desirable to provide a fluid device wherein the attendant noise and vibration levels are significantly reduced.